NTSB Safety Recommendation P-06-005

NTSB safety recommendation P-06-005.

The National Transportation Safety Board recommends that the Plastics Pipe Institute: Revise your butt-fusion joining procedure for plastic gas pipe to (1) stress the importance of inspecting the finished joint, (2) include guidance on the joining of coiled pipe, and (3) include a requirement for the avoidance of mitering.

Priority: CLASS II

Overall Status: Closed - Acceptable Action

Issued Date: 2006-06-08

Adopted Date: 2006-05-31

Overall Date Closed: 2008-03-17

Synopsis: On August 21, 2004, about 8:54 a.m., a natural gas explosion destroyed a residence located at 48 Woodland Lane in DuBois, Pennsylvania. Two residents were killed in this accident. The Safety Board determined that the probable cause of the leak, explosion, and fire in DuBois, Pennsylvania, on August 21, 2004, was the fracture of a defective butt-fusion joint and the failure of the National Fuel Gas Distribution Corporation to have an adequate program to inspect butt-fusion joints and replace those joints not meeting its inspection criteria.

Probable Cause: The National Transportation Safety Board determines that the probable cause of the leak, explosion, and fire in DuBois, Pennsylvania, on August 21, 2004, was the fracture of a defective butt-fusion joint and the failure of the National Fuel Gas Distribution Corporation to have an adequate program to inspect butt-fusion joints and replace those joints not meeting its inspection criteria.

Ntsbnumber: DCA04MP006

Report Number: PAB-06-01

Addressee Name: Plastics Pipe Institute

Addressee Status: Closed - Acceptable Action

Addressee Date Closed: 2008-03-17

Addressee Acronym: PPI

Addressee Organization Type: A-Associations

Communication Date: 2007-10-26

Communication Type: Official Correspondence

Communication Contents: Letter Mail Controlled 11/26/2007 11:54:04 AM MC# 2070691: 10-26-07: In a letter from the National Transportation Safety Board dated June 8, 2006, the following safety recommendations were made to the Plastics Pipe Institute regarding revisions to PPI technical report TR-33 Generic Butt Fusion Joining Procedure for Field Joining of Polyethylene Pipe; Revise your butt-fusion joining procedure for plastic gas pipe to (1) stress the importance of inspecting the finished joint, (2) include guidance on the joining of coiled pipe, and (3) include a requirement for the avoidance of mitering. In response to this recommendation, the PPI has revised TR-33 in the following manner: 1. Added the following to address point (1) - importance of inspecting finished joint Visual Inspection Visually inspect and compare the joint against the manufacturer’s recommended appearance guidelines. Visually, the width of buff fusion beads should be approximately 2 to 2-1/2 % times the bead height above the pipe and the beads should be rounded and uniformly sized all around the pipe circumference. The v-groove between the beads should not be deeper than half the bead height above the pipe surface. When butt fusing to molded fittings, the fitting-side bead may display shape irregularities such as minor indentations, deflections and non-uniform bead rollover from molded pad cooling and knit lines. In such cases, visual evaluation is based mainly on the size and shape of the pipe-side bead. (See Appendix D for bead configuration). Visually unacceptable joints should be cut out and re-fused using the correct procedure. (See manufacturer's visual inspection guidelines). 2. Added the following to address points (2) and (3) - guidance on coiled pipe and avoidance of mitered joints: [See Figure A-7 Visually unacceptable mitered joint] Visually mitered (angled, off-set) joints should be cut out and re-fused (straight or coiled pipe). Coiled pipe is available in sizes through 6” IPS. Coiling may leave a bend in some pipe sizes that must be addressed in the preparation of the butt fusion process. There are several ways to address this situation: 1. Straighten and re-round coiled pipe before the butt fusion process. (ASTM02573 requires field re-rounding coiled pipe before joining pipe sizes larger than 3” IPS.) 2. If there is still curvature present, install the pipe ends in the machine in an “S” configuration with print lines approximately 780” apart in order to help gain proper alignment and help produce a straight joint. See Figure A2 3. If there is still a curvature present, another option would be to install a straight piece of pipe between the two coiled pipes. Every effort should be made to make the joint perpendicular to the axis of the pipe. Figure A-2 Alignment of Coiled Pipe Ends Through a Butt Fusion Machine These revisions have been incorporated into the latest version of TR-33 (TR-33/2006). In addition, the TR-33 generic butt fusion procedures are being incorporated into a new ASTM Standard Practice F 2620, and will include this information as well.

Addressee Acronym: PPI

Addressee Organization Type: A-Associations

Communication Date: 2008-03-17

Communication Type: Official Correspondence

Communication Contents: Because PPI technical report TR-33, Generic Butt Fusion Joining Procedure for Field Joining of Polyethylene Pipe, has been revised to (1) address the importance of inspecting finished joint, (2) provide guidance on coiled pipe, and (3) address avoidance of mitered joints, Safety Recommendation P-06-5 is classified Closed Acceptable Action.